Answered

It's merely a role-play game that some users play. I confess that, when I was just a few days new to Second Life, I was tricked into accepting a bite and I found it a rather unpleasant experience. A message appeared on my screen telling me that I had lost ten percent of my humanity and, in my inexperience, I honestly thought that, if I were bitten nine more times, I would lose my account. This was, of course, untrue and I soon found a free garlic necklace that removed me from their "game." I would suggest that you search the marketplace and do likewise. Most importantly, there are no ill effects in being bitten.

Answered

If you allow a vampire to bite you in Second Life, your avatar will suffer no after-effects. You may, however, find that the person who bites you might also want you to become a vampire or to join their "clan", and you have no obligation to join anything at all.

I allowed my avatar to be bitten by a vampire in 2007, and I have suffered no after effects...

... oh, except I do get the urge to howl at the moon when it is full (but only in RL )